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howtos:misc:proxying_smtp [2015/11/27 23:41 (UTC)]
louigi600 [Proxying Emails to Your Local Mail Relay Server]
howtos:misc:proxying_smtp [2016/06/20 07:28 (UTC)] (current)
alienbob proxying_smtp renamed to howtos:misc:proxying_smtp (Ended up in the wrong namespace)
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 Here are some scenarios with examples on how you could go about working around the problem. Here are some scenarios with examples on how you could go about working around the problem.
  
-Throughout the scenarios we will be referring so 3 machines:+Throughout the scenarios we will be referring to 3 machines:
  
   * Machine A with IP address 192.168.0.2 (cannot send mails directly via internet and cannot relay on Local Mail Relay)   * Machine A with IP address 192.168.0.2 (cannot send mails directly via internet and cannot relay on Local Mail Relay)
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   * Machine B can reach LMR's port 25   * Machine B can reach LMR's port 25
  
-We can use nc on Machine B to proxy mail from A to LMR+We can use nc on Machine B to proxy mail from A to LMR. In this example it will appear to LMR as if it was Machine B that is sending the email.
  
 On machine B On machine B
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   * Machine A can reach the LMR but only on port 22.   * Machine A can reach the LMR but only on port 22.
  
-We use a ssh tunnel between A and LMR to do the job for us.+We use a ssh tunnel between A and LMR to do the job for us. In this example we are bypassing firewall by using ssh to forward traffic trough a encrypted tunnel. For this to work properly the ssh client that is going to be forwarding needs to be executed by an administrative account.
  
 <note important>This time we will be working exclusively on machine A</note> <note important>This time we will be working exclusively on machine A</note>
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   DATA   DATA
   354 End data with <CR><LF>.<CR><LF>   354 End data with <CR><LF>.<CR><LF>
-  FROM:drao@invallee.it +  FROM:me@localnet.com 
-  TO:drao@invallee.it+  TO:dude@localnet.com
   SUBJECT:test using ssh tunnel   SUBJECT:test using ssh tunnel
   if you get this sending email trough ssh tunnel worked   if you get this sending email trough ssh tunnel worked
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 We can then start the ssh socks proxy on Machine B listening on a port Machine A can access: We can then start the ssh socks proxy on Machine B listening on a port Machine A can access:
  
-On machine B+On machine B with a privileged user
   ssh -2 -D 192.168.1.2:1024 -N  192.168.2.2 &   ssh -2 -D 192.168.1.2:1024 -N  192.168.2.2 &
  
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   DATA   DATA
   354 End data with <CR><LF>.<CR><LF>   354 End data with <CR><LF>.<CR><LF>
-  FROM:drao@invallee.it +  FROM:me@localnet.com 
-  TO:drao@invallee.it+  TO:dude@localnet.com
   SUBJECT:test using ssh tunnel   SUBJECT:test using ssh tunnel
   if you get this sending email trough ssh tunnel worked   if you get this sending email trough ssh tunnel worked
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 We can still get the whole command to run on the LMR via ssh: We can still get the whole command to run on the LMR via ssh:
 +
 +<note important>This time we will be working exclusively on machine A</note> 
  
   cat << EOF > send_this_mail   cat << EOF > send_this_mail
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 ====== NOTES ====== ====== NOTES ======
-The command we used above is probably a good example of bad unixcraft, let me give a brief explanation on how it works.+The command we used in Scenario 1 is probably a good example of bad unixcraft, let me give a brief explanation on how it works.
 Let's momentarely get rid of the odd use of the fifo by just using this: Let's momentarely get rid of the odd use of the fifo by just using this:
  
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 so now the whole command line looks like this: so now the whole command line looks like this:
   cat /tmp/f | nc -l -p 1234 -s 192.168.1.2 | nc 192.168.2.2 25 >> /tmp/f   cat /tmp/f | nc -l -p 1234 -s 192.168.1.2 | nc 192.168.2.2 25 >> /tmp/f
-it is possible to do the same thing without having to use cat it is a little neater but still bad unixcraft+it is possible to do the same thing without having to use catit is a little neater but still bad unixcraft
   nc -l  -p 1234 -s 192.168.1.2 < /tmp/f |nc 192.168.2.2 25 >> /tmp/f   nc -l  -p 1234 -s 192.168.1.2 < /tmp/f |nc 192.168.2.2 25 >> /tmp/f
  

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